I have a black skirt tetra who has been "bodyslamming" my cories when they're eating their algae wafers. he comes over and knocks them off with the side of his body. Then he steals the wafer and hides it! I also just noticed a white almost fuzzy looking mark on one of my bronze cories. Could this be a bite mark or perhaps some sort of itch or fungus? I have never dealt with any type of fish illness before. Any help would be appreciated. Thanks.